Traditionally, online content or an information resource (e.g., an internet web page) was associated with a predefined list of content items, such as a list of news items, jobs, search results, etc. If, after viewing all of the content items associated with an information resource, a user wanted to view additional related content items, the user would typically navigate (e.g., click a link) to an additional information resource that included an additional list of the additional related content items. Thus, content items corresponding to a particular subject (e.g., Google search results) were separated into lists that were distributed across multiple information resources. In such an environment, advertisement placement was often simply a matter of associating different advertisements with each information resource. For example, a first set of advertisements were associated with a first web page (e.g., based on a relationship between the first set of advertisements and the content items associated with the first web page), a second set of advertisements were associated with the second set of web pages, and so on. Then, when a user navigated from a first web page to a second web page, different advertisements were presented to the user.
However, some information resources are configured to grow dynamically and continually. These information resources may appear to be bottomless or infinite to a user. For example, a user may access a web page that includes what appears at first to be a static list of content items. However, when the user scrolls down to the bottom of the web page, additional content items may be appended to the list of content items associated with the web page. When the user scrolls down to the bottom of the web page again, even more content items may be appended to the list. And so on. The list of content items associated with such an information resource may grow almost indefinitely. In this case, the user need not navigate from a first information resource to a second information resource to view an additional list of content items. For such dynamically growing information resources, management of advertising presented in conjunction with the information resources may become a complex problem.